OBJECTIVES: To determine similarities and differences in the reasons for using or not using complementary and alternative medicine (CAM) amongst general and condition-specific populations, and amongst populations in each region of the globe. METHODS: A literature search was performed on Pubmed, ScienceDirect and EMBASE. KEYWORDS: 'herbal medicine' OR 'herbal and dietary supplement' OR 'complementary and alternative medicine' AND 'reason' OR 'attitude'. Quantitative or qualitative original articles in English, published between 2003 and 2018 were reviewed. Conference proceedings, pilot studies, protocols, letters, and reviews were excluded. Papers were appraised using valid tools and a 'risk of bias' assessment was also performed. Thematic analysis was conducted. Reasons were coded in each paper, then codes were grouped into categories. If several categories reported similar reasons, these were combined into a theme. Themes were then analysed using χ tests to identify the main factors related to reasons for CAM usage. RESULTS: 231 publications were included. Reasons for CAM use amongst general and condition-specific populations were similar. The top three reasons for CAM use were: (1) having an expectation of benefits of CAM (84% of publications), (2) dissatisfaction with conventional medicine (37%) and (3) the perceived safety of CAM (37%). Internal health locus of control as an influencing factor was more likely to be reported in Western populations, whereas the social networks was a common factor amongst Asian populations (p < 0.05). Affordability, easy access to CAM and tradition were significant factors amongst African populations (p < 0.05). Negative attitudes towards CAM and satisfaction with conventional medicine (CM) were the main reasons for non-use (p < 0.05). CONCLUSIONS: Dissatisfaction with CM and positive attitudes toward CAM, motivate people to use CAM. In contrast, satisfaction with CM and negative attitudes towards CAM are the main reasons for non-use.